Oil consumption

My 2005 pacifica recently started consuming roughly 1 quart of oil every 2,000-3,000 miles. It got drastically low back in June between oil changes and the techs told me I was down to less than a quart of oil. At that time, I had a noisy engine, but I never had any indicator lights that I was hot, or low in oil. The mechanics told me they thought the cause was that at my last oil change (not done by them) they didn't put enough oil in the car.

Well, now one month later it is still doing the same thing, I have been very careful about checking it now that I am suspicious about it. This car has 36, 100 miles on it. It is not leaking, nor do I consistently see smokey exhaust, although I have seen it rarely right after I start it up and it idles for a few minutes.

Do you have any ideas on what could cause this? If it is not fixed, is there any long term damage that can be done to the engine due to this consumption of oil?